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CU-Boulder's Student Dust Counter reports clean Pluto environment

Very few dust grains detected during New Horizons flyby of dwarf planet

By Charlie Brennan

Staff Writer

Posted:
03/17/2016 02:00:00 PM MDT

Updated:
03/17/2016 02:00:15 PM MDT

The Student Dust Counter, an instrument designed and built by University of Colorado students, is flying on the New Horizons spacecraft that passed by Pluto last July, and is helping scientists better understand the evolution of the solar system. (NASA / Courtesy image)

As the New Horizons spacecraft continues hurtling through the distant Kuiper Belt, fruits from its historic flyby last year of Pluto continue to be analyzed. And what hasn't been found interests scientists nearly as much as other aspects of their resulting discoveries.

In a paper published today in Science, it is reported that data downloaded and analyzed by the New Horizons team showed that the environment surrounding Pluto and its moons contained only about six dust particles per cubic mile.

CU professor Fran Bagenal, who leads the New Horizons Particles and Plasma Team, said the scant space dust, considered the building blocks of planets, in Pluto's neighborhood was unexpected.

"It is surprising that you have a system that's got five moons, some of them quite small, so you think there must be debris that is being kicked out when the system was formed, or as things bashed into it," Bagenal said.

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"And yet we find it so clear of debris. It may be that is telling us this system has been around for some time, and this dust has been cleared away. These are all new things that we had not thought about before," she said. ".... We're scratching our heads and trying to work out what's going on."

The Student Dust Counter is described in a university news release as a thin film resting on a honeycombed aluminum structure about the size of a cake pan, affixed to the exterior of the spacecraft. A small electronic box assesses each individual dust particle that hits the detector, enabling students to infer the mass of each particle.

More than 20 CU students, mostly undergraduates, worked on designing and building the dust counter for New Horizons between 2002 and 2005. Several students and researchers are currently assessing the flyby data.

Bagenal said that the absence of dust for the dust counter to count in no way registered as a disappointment for researchers.

"I think the subjective interpretation is relief, because it meant that the spacecraft could survive, and get through," she said. "We were seriously worried that we would hit a major debris that would damage the spacecraft."

The study published today was led by Bagenal and involved more than 20 other researchers, including LASP physics professor Mihaly Horanyi; CU doctoral student Marcus Piquette of the Department of Astrophysical and Planetary Sciences; and Southwest Research Institute postdoctoral researcher Jamey Szalay, who received his doctorate in physics from CU under Horanyi last year.

Despite the largely dust-free trip past Pluto — the baby piano-sized spacecraft came within 7,700 miles at its closest point — Horanyi, the principal investigator for the Student Dust Counter, said it logged thousands of dust grain contacts during the spacecraft's epic nine-year, 3-billion-mile journey to Pluto.

"Now we are now starting to see a slow but steady increase in the impact rate of larger particles, possibly indicating that we already have entered the inner edge of the Kuiper Belt," Horanyi said in the news release.

New Horizons continues to speed through the Kuiper Belt, covering about 750,000 miles a day. Its next — and final — target is a 30-mile-diameter object named 2014 MU69, which the spacecraft is expected to pass in January 2019.

"It keeps going and going, and we should able to keep measuring the solar wind and the energetic particles for some time beyond that, maybe 15 or 20 years," Bagenal said.

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